1. Field of the Invention
This invention relates to an apparatus for transferring particulate material such as powder granules and the like (referred to herein as "powders") from a bulk supply to flexible containers such as bags.
2. Discussion of Related Art
The transfer of powders from a bulk supply to smaller containers for marketing or storage is complicated by the fact that the flow characteristics of powders are very different from those of liquids. For example, some powders tend to be sticky and flow only with difficulty while others may be of very light and flocculent nature so that when they are poured into a container, displaced gas such as air carries with it substantial quantities of entrained powder. This can cause fire hazards if powder is flammable or financial loss or danger to health if the powder is expensive or toxic.
The filling of a large number of containers with powder from a bulk supply must for practical reasons be carried out rapidly and under conditions so that, preferably, the escape of powder is prevented or, if this is not possible, then efficient methods of powder recovery are employed. Various measures have been taken for the purposes of achieving this objective. For example, one of these involves fitting the delivery end of a filling head, which extends from the bulk supply of powder to the container to be filled with an inflatable annulus which may grip and form an air-tight seal with the mouth of the container when inflated. The powder is fed via a first conduit in the filling head. A second conduit is provided through which displaced gas containing entrained powder can pass on its way to a powder recovery station where powder can be recovered. In order to assist the process, a draught created by an exhaust fan assists the removal of displaced gas. However, in order to avoid any excessive reduction in pressure within the container, air from outside the container is allowed to enter the container, through a third conduit and merge with the effluent stream of gas leaving the container. In this way, an improvement has been effected. However, even with existing well designed machines, there is a tendency for small quantities of powder to escape.
Typical prior apparatuses for filling containers are represented by U.S. Pat. Nos. 5,052,451(Gentilcore), 3,258,041 (Lau), 4,312,388 (Hager) and 3,384,134 (Hillerns).
Gentilcore describes both exhausting of displaced gases by an extraction fan and the introduction of purge gas for flammable or reactive products. There is also described a filter in the path of the exhausted gas. It does not describe, however, the use of an ambient venting conduit, nor any means for cleaning the filters.
Hager uses nitrogen as a purge gas and also powered air extraction. Again, however, there is no direct vent to atmosphere and no means of cleaning filters.
Both Lau and Hillerns describe filling systems whereby filters are cleaned by reverse flow. Neither, however, addresses the problem of achieving such filter cleaning in combination with inert gas purging.